The goal of the project is to gain knowledge of stimulus factors that control verbal learning processes in normal children and retarded individuals. Process analysis of the verbal learning behaviors of mentally retarded persons is conceptualized within a developmental rather than a pathological orientation. The purpose is to specify the ways in which the verbal learning of retarded persons is impaired and the circumstances under which these disabilities are manifested. The specific focus of this research is on the control process of stimulus selection. Experiments are planned to determine the factors that control stimulus selection and the conditions under which stimulus selection serves adaptive functions. The primary tasks to be used are paired-associates and verbal discrimination learning. The major independent variables include cue saliency, meaningfulness, stimulus context, induced interference, cue reinforcement history, degree of learning, and level of mental development. The primary dependent variables are learning rate, transfer recall, and consistency and efficiency of stimulus selection. These variables, both on the independent and dependent sides, are couched within a variable encoding theory of associative learning.